Don't double-zero buffers in fault management nvlists

This is a small cleanup for a trivial problem which happened to
be noticed while another issue was being investigated.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Paul Dagnelie <pcd@delphix.com>
Closes #13730

module/zfs/fm.c

@@ -487,7 +487,7 @@ static void *
 i_fm_alloc(nv_alloc_t *nva, size_t size)
 {
 	(void) nva;
-	return (kmem_zalloc(size, KM_SLEEP));
+	return (kmem_alloc(size, KM_SLEEP));
 }
 
 static void